Inverse Ionic Peak with a MS Ion Trap

[problemeste]

Hi,

we carry out an analysis of API and we get a Total Ion Chromatogram with a inverse ionic peak...we have never seen before and we are wondering why?? Does anyone have any idea about it?

Thanks!

[bhuvfe]

Do you mean a negative chromatographic peak?

Maybe try posting a picture of what you see.

[lmh]

In LC-MS, if that's where you are, a negative peak usually happens in an extracted ion chromatogram of a mass that happens to be present as a background ion, where something else elutes at a particular retention time, and cosuppresses the background ion at that point.

[problemeste]

Thank you very much for you quickly answer!

I can't attach it...or maybe i have no idea. Please send me ur email and i send u the chromatogram (TIC, EIC , UV).

[problemeste]

I've gotten it to work!

http://img692.imageshack.us/i/dibujoed.gif/

So here u can show it!

[bhuvfe]

As lmh mentioned a negative peak in LC-MS is created by ion suppression of the background ions due to the passing of your analyte. For compounds that don't ionize well this is relatively common (at least for my analytes). Unless you find a way to decrease the background (or improve the ionization of the peak at 11.2 min) there's probably nothing you can do to avoid this.

But considering that you have quite a decent peak in the EIC and that many instruments have software to dig up peaks out of the noise you can use the data easily.